(n,α) reactions cross section research at IPPE

¹ IPPE, Institute of Nuclear Physics Problems in Nuclear Engineering, 249033 Obninsk, Russia
² National Research Nuclear University MEPhI, Obninsk Institute for Nuclear Power Engineering of NRNU MEPhI, Obninsk, Russia.
³ EU JRC – Institute for Reference Material and Measurements, Geel, Belgium.

^a e-mail: hva@ippe.ru

Abstract

An experimental set-up based on an ionization chamber with a Frisch grid and wave form digitizer was used for (n,α) cross section measurements. Use of digital signal processing allowed us to select a gaseous cell inside the sensitive area of the ionization chamber and determine the target atoms in it with high accuracy. This kind of approach provided us with a powerful method to suppress background arising from the detector structure and parasitic reactions on the working gas components. This method is especially interesting to study neutron reactions with elements for which solid target preparation is difficult (noble gases for example). In the present experiments we used a set of working gases which contained admixtures of nitrogen, oxygen, neon, argon and boron. Fission of ²³⁸U was used as neutron flux monitor. The cross section of the (n,α) reaction for ¹⁶O, ¹⁴N, ²⁰Ne, ³⁶Ar, ⁴⁰Ar and the yield ratio α₀/α₁ of ¹⁰B(n,α₀) to ¹⁰B(n,α₁) reactions was measured for neutron energies between 1.5 and 7 MeV. Additionally a measurement of the 50Cr(n,α) cross section using a solid chromium target is also reported.